Liquid-liquid extraction is a commonly employed technique for transferring a solute dissolved in a first liquid to a second liquid that is essentially immiscible with the first liquid. The solution of the solute in the first liquid is generally termed a “feed solution”, and the second liquid is generally termed an “extractant” or “liquid extractant”. The solute tends to distribute itself between the two liquids in accordance with the relative solubility of the solute in the two liquids when the feed solution is brought into contact with the liquid extractant.
One conventional approach to achieving liquid-liquid extraction is to directly mix the feed solution and the liquid extractant. Unfortunately, this technique often times gives rise to the formation of a persistent dispersion or emulsion within the mixture, rendering the extraction process highly inefficient, in terms of both time and end result.
A microporous membrane extraction methodology has been developed to address the above-identified dispersion concerns. In particular, one side of a microporous membrane is typically contacted with the feed solution, and the opposing side of the microporous membrane with the liquid extractant. A liquid-liquid interface, across which the solute is transferred, is thus formed between the feed solution and the liquid extractant within micropores of the microporous membrane.
The concept of providing gross separation between the feed solution and the liquid extractant via a microporous membrane has proven to be viable. However, the viability of microporous membrane liquid-liquid extraction in an industrial setting typically depends on the rate of extraction (that in turn is a function of the liquid-liquid interface surface area provided by the microporous membrane) and on the ease of replacing the membrane, should it become damaged or fouled. Conventional microporous membrane liquid-liquid extraction apparatuses and methods utilize designs with limited liquid-liquid interface surface area, and that do not facilitate membrane replacement. These inherent inefficiencies have impeded the large scale, commercial implementation of microporous membrane extraction.
Many commercial applications, such as obtaining ethanol from a fermented feed broth, could greatly benefit from the use of a microporous membrane liquid-liquid extraction technique. As such, a need exists for a high productivity liquid-liquid extraction system and method incorporating a microporous membrane adapted to be maintained on a cost effective basis.